SeaWorld Parks and Entertainment, which is exploring a sale, has attracted early buyout interest from private equity firm Apollo Global Management LLC and amusement park operator Six Flags Entertainment Corp, according to three people familiar with the matter.

Apollo, which got into the resort and leisure business with its $262 million acquisition of Great Wolf Resorts in 2012, and Six Flags, the largest regional theme park operator in the world, are among several potentially interested parties, according to the sources.

The process is largely limited to a small group of industry players that have experience in the sector, one source said.

A deal could value SeaWorld, known for its killer whale mascot Shamu, at about $4 billion, based on the financials of its publicly listed peers, such as Six Flags and Cedar Fair LP .

Blackstone acquired SeaWorld from beer giant Anheuser-Busch InBev SA for $2.3 billion in December 2009, according to Blackstone’s website.

Blackstone and Apollo declined to comment, while Six Flags was not immediately available. The sources asked not to be named because the process is not public.

A public offering for SeaWorld remained the more likely route since it would come at a time when shares for amusement park operators are trading at healthy levels, one source said.

Established operators in the U.S. theme park industry host about 315 million visitors per year and have proven resilient in a weak economy as parents still turn to them for family vacations.

SeaWorld owns 11 theme parks, including those with the SeaWorld, Busch Gardens and Sesame Place brands, and cares for more than 67,000 animals. (Reporting by Soyoung Kim and Olivia Oran in New York; Editing by Jeffrey Benkoe)